Method of preserving unseasoned wood or lumber



United States Patent Ofifice 3,053,730 Patented Sept. 11, 1952 3,053,730 METHGD 6F PRESERVING UNSEASONED WOOD QR LUMBER Ragnar Teodor Birgersson Winbladh, Stockholm, Sweden, assignor to British Petroleum 'Co., Limited, London, England, a company of Great Britain No Drawing. Filed Aug. 20, B59, Ser. No. 834,917 Claims priority, application Sweden Oct. 23, 1958 3 Claims. (Cl. 167-385) This invention relates to a new method of impregnating green lumber or unseasoned or damp wood in order to protect the same against attack and damages from biological organisms, for instance microorganisms such as fungi, and insects.

For many years it has been the practice to impregnate wood against the attack of fungi, such as rot, blue stain, other microorganisms and also insects, with different kinds of preservatives, so called fungicides and insecticides, e.g. pentachlorophenol, monochloronaphthalene, orthodichlorobenzene and their derivatives. But also phenols, naphthalenes and oxyquinolines and their derivatives have been used for this purpose.

These preservatives are insoluble in water and they have therefore been used in solutions in organic solvents such as oils from petroleum or from the distillation of coal. Such solvent oils are miscible with water. It is obvious that such preserving liquids can only be used for impregnating dry wood or wood having a very low moisture content, whereas at higher water contents, as in the case of green lumber or unseasoned wood, the water prevents the impregnating liquid from penetrating into the wood. Attempts have been made to improve the penetration into damp wood of the liquids in question by the addition of agents which reduce the surface tension, but also by this means only an insufliciently thin surface layer was impregnated. Emulsions containing a preservative have also been used with a certain, though not satisfactory, protective effect.

For the impregnation of green lumber or unseasoned wood one has therefore hitherto had to resort to the use of aqueous solutions of water-soluble preserving agents. The disadvantage with the use of such water-soluble preservatives is that the preservative is easily soaked out of the wood again by water, e.g. in rain or during floating. Thus, the very important problem of impregnating the lumber in combination with the timber cutting in the forest so as to obtain a protection against the attack by biological organisms during storage and transportation to the saw mills, pulp mills or other industries for the exploitation of wood can be regarded as practically unsolved.

The present invention now gives a solution to this problem.

According to the invention a solution is prepared containing a preservative which is substantially insoluble in water and which is dissolved in a solvent which is miscible with water and the green lumber or unseasoned wood is treated with that solution. The term unseasoned wood refers to wood having a moisturecontent above the saturation point of the Wood fibres, i.e. above 25%, calcu- 6 lated on the dry substance of the wood. The treatment preferably takes place at ordinary temperature. Such a solutionhas no difliculty in penetrating into damp wood but is not soaked out again with water, e.g. during rain or floating, since water being soaked into the impregnated wood will dilute the solvent thereby decreasing the solubility of the preservative so that it is precipitated within the wood. Such precipitation, of course, can also occur during the impregnation process when the impregnation liquid penetrating the wood is sufiiciently diluted with the water content of the wood.

It has been previously known that water-miscible liquids such as acetone, methyl alcohol, and ethyl alcohol are solvents for water-insoluble wood preservatives, e.g. pentachlorophenol, and such solutions have also been suggested for the impregnation of wood, but only for dry wood and never for damp wood, such as green lumber and unseasoned wood. Probably, if anyone has had the idea of trying such solutions on damp wood he has immediately abandoned it under the impression that the contact between such solutions and the water of the wood would immediately cause precipitation of the preservative on the wood surface, thus prohibiting the penetration into the wood. The inventor of this invention has overcome such preconceived ideas and found that such solution penetrates into the damp wood satisfactorily without any disturbances due to precipitation of the preservative.

-As is understood from the above in principle any prescrvative which is insoluble in Water but soluble in a solvent which in turn is miscible with water can be used according to the invention.

Examples of such water-insoluble preservatives are:

phenols and their derivatives, such as penta-chloro ing reason:

Diacetone alcohol has a high boiling point, its flash point is high, 52 C. (P.M.), and its vapour pressure at 20 C. is proportionately very low, namely 0.8 mm. Hg. For comparison it may be mentioned that the vapour pressure at 20 C. for ethyl alcohol is 43 mm. Hg and its flash point (Abel) is 12 C., and that acetone has a vapour pressure of 184 mm. Hg at 20 C. and a flash point (Abel) of -17 C. The low vapour pressure means that the diacetone alcohol evaporates very slowly from the interior of the wood and will remain in the wood during a long time. The wood fibres will therefore be surrounded by a film of the solvent containing dissolved preservative.

In case the impregnating liquid has been diluted with the water in the wood so far that the preservative begins to precipitate, it would appear that it precipitates in the form of an oily phase which surrounds the wood fibres. In both cases the preserving effect obtained is very good.

The problem of impregnating green wood is of great importance, for example when felling aspen trees for manufacturing matches. The cut surface of the newly felled aspen logs oifer good soil for various microorganisms, which rapidly spread into the wood. By impregnating the cut surfaces one can, indeed, prevent the harmful microorganisms from penetrating into the wood, but this impregnation must be done almost immediately after the sawing. The cut surface is then so damp that entirely oil based impregnating solutions mentioned cannot be used, and water soluble impregnating agents have, as said before, the disadvantage of being Washed out, e.g. with rain or when floating, before the logs are sawn. If impregnation is postponed until the logs have dried sufficiently to permit oily impregnating liquids to be used, the microorganisms have already had time to penetrate deep into the wood, which leads to considerable loss of timber.

According to the method of the invention, the cut sur- 3 faces of the logs are preferably impregnated already at the working place immediately after the felling, and the preservative which has penetrated into the Wood is not washed out during the transport of the logs to the factory and the subsequent storage.

In the case when trees are felled at a temperature not above C., impregnation according to the invention can be postponed until the logs have been brought together at a larger place of deposit, e.g. loaded on vehicles.

It has further been found possible to replace part of the water-miscible solvent in the preserving liquid with an oil, for instance a vegetable oil such as linseed oil, but preferably a petroleum oil, without impairing the good preserving properties. It is surprising that the excellent penetration ability in damp wood does not disappear when adding the water-insoluble oil. This fact is especially surprising when a large quantity of oil is added, for instance, when at least half the quantity of Water-miscible solvent has been replaced by petroleum oil.

The presence of an oil makes the impregnated wood more or less water-repellent, and thereby the risks of cracks occurring in the wood are diminished when during its use it is exposed to alternating damp and dry surroundings.

As petroleum oil we prefer to use an oil corresponding to fuel oils No. 1 to 4 according to ASTM D 396.

When preparing the preserving liquid according to the invention, containing petroleum oil, it may be found that the petroleum oil is not fully miscible with the water-miscible solvent in the desired ratio, but two phases are formed in the liquid especially at a low temperature. The remedy for this inconvenience is to add a small quantity of a surface active agent or an auxiliary solvent which, in a manner known per se, makes the two phases miscible with each other to form a stable solution.

Example 1 A solution was prepared containing 90% by weight diacetone alcohol and by weight penta-chlorophenol. This solution was applied by means of a brush onto the cut surfaces of a log immediately after the tree had been felled.

Example 2 A solution was prepared containing 90% by weight ethyl alcohol and 10% by weight penta-chloro-phenol. This solution was sprayed on the cut surfaces of a log shortly after the tree had been felled.

Example 3 parts by weight penta-chloro-phenol were dissolved in 100 parts by weight diacetone alcohol, and 200 parts by weight fuel oil No. l were admixed. The liquid was somewhat turbid. 100 parts by weight linseed oil were admixed, yielding a clear solution having good properties for the preserving of wood.

Example 4 A solution was prepared containing:

2.3% by weight ortho-dichloro-benzene 2.3% by weight mono-chloro-naphthalene 11.6% by weight penta-chloro-phenol 9.3 by weight ethyl alcohol 74.5% by weight fuel oil No. 1

Blocks of green pine wood were dipped into said solution at normal temperature for 10 seconds, and were then allowed to dry for 5 minutes. The blocks were then tested with respect to their resistance against attacks by the fungi Leptographium, Cladosporium, Trichoderma, Stereum sanguinolentum and Lentinus lepideus. The solution gave an excellent protection: no damage could be seen on any pine block.

4: Example 5 A solution was prepared containing:

1.3% by weight ortho-dichloro-benzene 1.3% by weight mono-chloro-naphthalene 6.5% by weight penta-chloro-phenol 5.2% by Weight diacetone alcohol 85.7% by weight fuel oil No. 1

Blocks of moist pine wood were treated with this solution and tested in the way described in Example 4. Also this liquid gave an excellent protection: no trace of decay could be seen on any block.

Example 6 Blocks of green pine wood were impregnated as described in Examples 4 and 5, and were allowed to dry for 5 minutes. They were then leached in running water for 6 hours and were then tested with respect to their resistance against attack by the microorganisms mentioned in Example 4. A trace of decay could be seen only on those blocks which had been tested with Trichoderma, whereas all other blocks were totally unaffected. Thus, the good protective effect still remains after leaching in water.

Example 7 In the solution described in Example 5 the diacetone alcohol was replaced by the same amount of butylcarbinol. The solution thus obtained remained stable at a lower temperature than the solution according to Example 5, and was consequently more suitable to be used in a cold climate.

As disclosed in Examples 5 and 7 the oil content may be as high as more than by weight of the total Weight of the composition. Owing to the fact that a composition having a high oil content gives a good protection, and owing to the fact that mineral oil is less expensive than the water-miscible solvents, we prefer to use as high an oil content as possible. It would appear that in most cases the ratio of water-miscible solvent to oil need not be higher than 1 to 9. The maximum oil content may easily be found experimentally for each specific combination of water-insoluble preservative, water-miscible solvent and oil.

I claim:

1. A method of preserving unseasoned wood against attack and damage by biological organisms, said unseasoned wood having a water content of above about 25% by weight on a dry basis, comprising: treating said unseasoned wood at atmospheric temperature and pressure with a treating solution containing penta-chlorophenol as a wood preservative and a water-miscible solvent which is a member selected from the group consisting of ethyl alcohol, diacetone alcohol, and butyl carbinol.

2. The method as claimed in claim 1, in which the treating is carried out on the cut surfaces of a log soon after the tree has been felled.

3. A method as claimed in claim 1, in which said solvent contains a petroleum oil corresponding to fuel oils No. 1 to 4 according to ASTM D396.

References Cited in the file of this patent UNITED STATES PATENTS 2,106,983 Klipstein Feb. 1, 1938 2,182,081 Hatfield Dec. 5, 1938 FOREIGN PATENTS 785,869 Great Britain Nov. 6, 1957 804,257 Great Britain Nov. 12, 1958 

1. A METHOD OF PRESERIVNG UNSEASONED WOOD AGAINST ATTACK AND DAMAGE BY BIOLOGICAL ORGANISMS, SAID UNSEASONED WOOD HAVING A WATER CONTENT OF ABOVE ABOUT 25% BY WEIGHT ON A DRY BASIS, COMPRISING: TREATING SAID UNSEASONED WOOD AT ATOMOSPHERIC TEMPERATURE AND PRESSUIRE WITH A TREATING SOLUTION CONTAINING PENTA-CHLOROPHENOL AS A WOOD PRESERVATIVE AND A WATER-MISCIBLE SOLVENT WHICH IS A MEMBER SELECTED FROM THE GROUP CONSISTING OF ETHYL ALCOHOL, DIACETONE ALCOHOL, AND BUTYL CARBINOL. 